Device and method for performing non-orthogonal multiplexing

ABSTRACT

A device includes circuitry configured to spread one or more symbols with one or more orthogonal codes into spread signals having a predetermined number of bits. The amplitude of the spread signals is modified via one or more layer coefficients and the spread signals are multiplexed into a layered transmit signal.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims the benefit of the earlier filing date ofU.S. provisional application 62/040,671 having common inventorship withthe present application and filed in the U.S. Patent and TrademarkOffice on Aug. 22, 2014, the entire contents of which being incorporatedherein by reference. In addition, the present application incorporatesby reference the entire contents of and claims the benefit of theearlier filing date of U.S. provisional application 62/052,291 havingcommon inventorship with the present application and filed in the U.S.Patent and Trademark Office on Sep. 18, 2014.

BACKGROUND

Technical Field

The present disclosure relates to communication using orthogonalfrequency division multiplexing (OFDM) for communications, and moreparticularly, to a multiplexing method.

Description of the Related Art

Recently, in addition to existing mobile phones, other wirelesscommunication devices have been developed. It is estimated that by theyear 2020, the demands on wireless communication resources will be onethousand times greater than the current wireless communication demands,which creates a need for new wireless communication resources, which canbe limited by restrictions within existing wireless communicationtechnologies. Within the 3GPP international standard for wirelesscommunication, a fifth generation (5G) standard has been developed,which further increases frequency utilization efficiency in order toaccommodate the increasing demands on wireless communication systems.

In the present LTE/LTE-A, orthogonal frequency-division multiplexing(OFDM) is employed, and multiplexing is performed using orthogonality inthe frequency domain. Further, carrier aggregation is used to increasewireless capacity by broadening bandwidth but does not solve the problemof radio wave resource depletion.

In some cases, the modulation order per subcarrier in OFDM is increasedin order to increase a total number of multiplexed symbols. For example,LTE uses 16QAM (quadrature amplitude modulation) and LTE-A uses 256QAM.In the case of LTE-A, the total number of transmitted bits persubcarrier increases to eight, but the distance between symbolsdecreases so that a higher energy per bit to noise power spectraldensity (E_(b)/N₀) is required to maintain a predetermined physicallayer bit error rate (PHY BER).

Other multiplexing methods have been introduced to solve the problemsintroduced by increasing the number of modulated bits per subcarrierthat include employing orthogonality relationships between the modulatedsymbols that include frequency, time and code. For example, OFDM isassociated with orthogonal frequencies, and CDMA is associated withorthogonal codes. In what is now considered to be fifth generation (5G)LTE, a filter bank multi carrier (FBMC) modulation method is used, whichemploys Wavelet OFDM. FBMC modulation makes a cycle prefix (CP)unnecessary by using time orthogonality and frequency orthogonalitytogether. In addition, a guard band is also unnecessary becauseout-of-band radiation is very low. FBMC modulation allows a largernumber of user equipments (UEs) to use identical bandwidths; however,the amount of improvement gained by eliminating the CP and guard band isat most ten percent, which is not enough to accommodate the increaseddemands on wireless communication systems.

In addition, non-orthogonal multiple access (NOMA) has also beenconsidered for solving the problems resulting from increased demands onwireless communication systems. NOMA allows multiplexed signals to beseparated at a receiver based on differences in signal-to-noise ratios(SNIRs) and allows transmitted signals to be multiplexed based onamplitude. For example, two signals can be multiplexed into a firstlayer and a second layer, and the transmitting power of the multiplexedsignal is determined based on achieving a SNIR for the first layer andthe second layer at the receiver that satisfies a desired BER. At thereceiver, the multiplexed layers are sequentially recovered bysubtracting a demodulated signal from the received signal. NOMA allowsfor greater amounts of multiplexing, but lower signal layers causeinterference with the higher layers, which causes an overall increase intransmit power, which can cause difficulties for terminal devices withlimited transmit powers. For example, two to three multiplexed layersare considered practical at this time.

In addition, NOMA uses a so-called adaptive modulation method to keepthe transmitting power in a cell or terminal device constant. Forexample, adaptive modulation allows the amount of modulation to bechanged based on the SNIR at the receiver. However, communication speedscan be very slow with adaptive modulation depending on the type ofmodulation being used, and frequency utilization efficiency can becomeeven worse.

SUMMARY

In an exemplary embodiment, a device includes circuitry configured tospread one or more symbols with one or more orthogonal codes into spreadsignals having a predetermined number of bits. The amplitude of thespread signals is modified via one or more layer coefficients and thespread signals are multiplexed into a layered transmit signal.

In another exemplary embodiment, a method includes spreading one or moresymbols with one or more orthogonal codes into spread signals having apredetermined number of bits; modifying an amplitude of the spreadsignals via one or more layer coefficients; multiplexing the spreadsignals into a layered transmit signal; and recovering received signallayers by reverse spreading a received signal with the one or moreorthogonal codes.

In another exemplary a device includes circuitry configured to recover ahighest received signal layer by reverse spreading a received signalwith the one or more orthogonal codes, re-spread the highest receivedsignal layer with one or more orthogonal codes and multiply acorresponding spread signal by an associated layer coefficient, andsubtract a re-spread signal from the received signal to recover one ormore lower received signal layers.

The foregoing general description of the illustrative embodiments andthe following detailed description thereof are merely exemplary aspectsof the teachings of this disclosure, and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of this disclosure and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1A is an exemplary block diagram of a transmitter, according tocertain embodiments;

FIG. 1B is an exemplary flowchart of a transmitter modulation process,according to certain embodiments;

FIG. 2A is an exemplary block diagram of receiver, according to certainembodiments;

FIG. 2B is an exemplary flowchart of a receiver demodulation process,according to certain embodiments;

FIG. 3A is an exemplary diagram of multiplexed layers, according tocertain embodiments;

FIG. 3B is an exemplary diagram of multiplexed layers, according tocertain embodiments;

FIG. 4A is an exemplary graph of bit error rate of a physical layer,according to certain embodiments;

FIG. 4B is an exemplary graph of bit error rate of a physical layer,according to certain embodiments;

FIG. 5 is an exemplary block diagram of a device, according to certainembodiments;

FIG. 6 is an exemplary schematic diagram of a data processing system,according to certain embodiments; and

FIG. 7 is an exemplary schematic diagram of a processor, according tocertain embodiments.

DETAILED DESCRIPTION

In the drawings, like reference numerals designate identical orcorresponding parts throughout the several views. Further, as usedherein, the words “a,” “an” and the like generally carry a meaning of“one or more,” unless stated otherwise. Furthermore, the terms“approximately,” “approximate,” “about,” and similar terms generallyrefer to ranges that include the identified value within a margin of20%, 10%, or 5%, and any values therebetween.

Aspects of the present disclosure are directed to a multiplexing methodfor increasing a number of multiplexed symbols for a modulated transmitsignal while maintaining predetermined bit error rate criteria. Theembodiments describe applying code multiplexing with an orthogonal codewith non-orthogonal multiple access (NOMA) techniques to increase atotal number of multiplexed symbols while simultaneously limiting anincrease in transmit power and frequency utilization efficiency.

FIG. 1A is an exemplary block diagram of a transmitter 100, according tocertain embodiments. The transmitter 100 includes an IFFT block 102 thatcomputes the IFFT for a signal that includes one or more subcarriers. Acycle prefix (CP) is added to the signal at the CP module 104, and aradio-frequency (RF) front end 106 converts the signal into radiofrequencies to be transmitted by an antenna 108.

FIG. 1A also shows a diagram of how the signal structure is constructedand transmitted by the transmitter 100. In some implementations, thetransmitter 100 includes associated circuitry that is configured toconvert a symbol into a spread signal having length L_(C) bits by usingan orthogonal code having a length of L_(C) bits. As the symbol isspread via the orthogonal code, the amplitude of the spread symbols isequal to 1/L_(C) of the amplitude of the original symbol. In oneimplementation, the orthogonal code used to spread the symbol is a Walshcode. Since the orthogonal code with L_(C) bits includes L_(C)orthogonal codes cd0 to cd(L_(C)−1), multiplexing is performed byspreading each of the L_(C) symbols via the L_(C) orthogonal codes cd0to cd(L_(C)−1) and adding the resultant spread symbols together. Themultiplexed symbols are then multiplied by a first layer coefficientcg0, which results in a first layer signal having L_(C) symbols.

Next, a second layer signal is obtained by multiplexing a new symbolinto spread symbols via the orthogonal code having L_(C) bits, addingthe resultant spread symbols together, and multiplying the spreadsymbols by a second layer coefficient cg1 to modify the amplitude of thesymbols, which results in a second layer signal having L_(C) symbols.The second layer signal is then multiplexed on to the first layersignal, and a total number of (L_(C)×M) symbols are multiplexed byrepeatedly performing the process of spreading, amplitude modification,and multiplexing onto previous layers up to an M^(th) layer.

According to one implementation, each of the M layers is spread usingthe same orthogonal code and one or the M-layers may not be orthogonalwith respect to the other layers. To be able to separate the M-layers ata receiver, the amplitudes of the layers are modified, which is referredto as Non-orthogonal Multiple Access (NOMA). In the present disclosure,the layer coefficients, cg0 to cg(L_(C)−1), are used to modify theamplitude values of each other M layers. Details regarding thedetermination of the layer coefficients are discussed further herein.

Once the 1^(st) layer to M^(th) layer signals have been multiplexed, thesignals are allocated to subcarriers. Since each of the signals up tothe M^(th) layer have been spread over the L_(C) bits, each of the L_(C)bits are allocated to a corresponding subcarrier for OFDM, which resultsin (L_(C)×M) symbols being multiplexed onto L_(C) subcarriers.Additional M-layer signals are allocated to subcarriers until allsubcarriers of the transmitter 100 have been allocated. In oneimplementation, a total number of subcarriers is represented by N_(sub),and a total number of symbols that can be transmitted by one IFFT of thetransmitter 100 is represented by the following equation:

$\begin{matrix}{{{Total}\mspace{14mu}{number}\mspace{14mu}{of}\mspace{14mu}{transmitted}\mspace{14mu}{symbols}} = {\frac{N_{sub}}{L_{C}} \times M \times L_{C}}} & (1)\end{matrix}$For example, the total number of transmitted symbols can be increased byincreasing the number of layers of the layered transmit signal and/orincreasing the number of subcarriers.

The total number of bits included in one symbol, N_(b), that can betransmitted by one IFFT of the transmitter 100 can be represented asfollows:

$\begin{matrix}{{{Total}\mspace{14mu}{number}\mspace{14mu}{of}\mspace{14mu}{transmitted}\mspace{14mu}{bits}} = {N_{b} \times \frac{N_{sub}}{L_{C}} \times M \times L_{C}}} & (2)\end{matrix}$

FIG. 1B is an exemplary flowchart of a transmitter modulation process120, according to certain embodiments. In one example, the number ofsubcarriers N_(sub) that can be handled by the IFFT block 102 of thetransmitter 100 is equal to 2048. In addition, a total number of layersM associated with the symbols to be multiplexed is equal to 4.

At step S122, a current layer value is initialized to a value of one. Atstep S124, a symbol to be transmitted is spread using orthogonal codesof length L_(C) bits. In one implementation, the orthogonal code that isused to modulate the transmitted symbols is a Walsh code having a lengthL_(C) of 4 bits, and the orthogonal code can be described as follows:cd0=(1,1,−1,−1)  (3.1)cd1=(1,−1,−1,1)  (3.2)cd2=(1,−1,1,−1)  (3.3)cd3=(1,1,1,1)  (3.4)Once the orthogonal code has been applied to the symbol, the resultantsymbols are added together. For example, as shown in FIG. 1A, data0,data1, data2, and data3 represent the spread symbols that aremultiplexed by orthogonal codes cd0, cd1, cd2, and cd3.

At step S126, the spread symbols are multiplied by a first layercoefficient cg0, which results in a first layer signal having L_(C)symbols. In one implementation, the layer coefficients, cg0 tocg(L_(C)−1), are used to modify the amplitude values of each other Mlayers. For example, because the layers are non-orthogonal with respectto one another, to separate the M-layers of transmitted signals at areceiver, each of the layers are multiplied by a value cg0 tocg(L_(C)−1), which distinguishes the layers from one another. To reduceinterference between the M layers, the values of cg for each of thelayers are determined such that a highest layer coefficient is greaterthan a sum of one or more remaining lower layer coefficients withrespect to the following equation:cg(M−1)>cg(M−2)+ . . . +cg0  (4)

For example, according to the example shown in FIG. 1A, the values ofcg0 to cg3 are determined as follows:cg0=1  (5.1)cg1=(1+dlt)  (5.2)cg2=(1+dlt)*2  (5.3)cg3=(1+dlt)*4  (5.4)The coefficient cg0 corresponds to the coefficient applied to the firstlayer symbols, cg1 is applied to the second layer symbols, cg2 isapplied to the third layer symbols, and cg3 is applied to the fourthlayer symbols. An optimum value of a coefficient difference factor, dlt,is determined based on a bit error rate (BER). For example, interferencebetween any two symbols can be reduced by increasing the value of thecoefficient difference factor, dlt. In addition, the value of dlt isless than 1 (dlt<1).

The determination of the amplitude values of the symbols described byequations (5.1) to (5.4) can more generally be illustrated by an exampleof a downlink (DL) from a base station to a terminal. For example, atotal number of multiplexed layers is equal to N is an integer andgreater than two, and an amplitude of a first layer is referred to asS1, the amplitude of each of the layers up to an N^(th) layer can berepresented by the following equations:1st Layer: S1=S1  (6.1)2nd Layer: S2=S1+dlt  (6.2)3rd to Nth Layers SM=2^(N-2)(S1+dlt)  (6.3)Therefore, the amplitude of the signal resulting from the multiplexingof all of the layers can be represented by the following:Sttl=Σ _(i=1) ^(N) S _(i)  (7)Thus, the equations (5.1) to (5.4) that describe layer coefficientvalues illustrate one exemplary implementation of equations (6.1) to(6.3) where S1 is equal to 1.

At step S127, the current layer is multiplexed onto the previous layers.For example, the second layer is multiplexed onto the first layer, thethird layer is multiplexed onto the first two layers, and the fourthlayer is multiplexed onto the first three layers. If the current layeris equal to one, then step S127 is skipped, and the process proceeds tostep S128.

In one implementation, based on equation (7) and the relationshipsdescribed above, a total amplitude resulting from all of the multiplexedlayers is 8*(S1+dlt), which is approximately eight times larger than asignal amplitude that results when no multiplexing is performed. Theincreased amplitude means that the transmitting power used to transmitthe layered, multiplexed signal also increases. According to someimplementations, when compared to an implementation where multiplexinghas not been performed, the transmitting power is increased by a factorof N when N multiplexing iterations are performed.

According to the embodiments described herein, the amplitude increasefrom the multiplexed layers may be mitigated due to the amplitudereduction that occurs when the signal is spread at step S122. Forexample, as the signals are spread to bits whose total number is L_(C)times as many bits as the total number of signals being transmitted,each of the bits has an amplitude that is 1/L_(C) times as large as theamplitude of each of the signals. Therefore, equation (7) can berewritten as follows:

$\begin{matrix}{{{Sttl}\mspace{14mu}{CD}} = {\frac{1}{L_{C}}{\sum\limits_{i = 1}^{N}S_{i}}}} & (8)\end{matrix}$

Because the amplitude of the signals is reduced by a factor of 1/L_(C)during the signal spreading at step S122, the overall amplitude of thetransmitted signal is also reduced by a factor of 1/L_(C). Therefore,the transmitter circuitry can be configured to modify a total transmitpower based on modifying at least one of a sum of the layer coefficientsor the predetermined number of bits of the spread signal. The SNIR ofthe signal at a receiver is unaffected by the amplitude reductionbecause as reverse spreading is performed, one symbol is formed byaccumulating the L_(C) bits. For example, if spreading is performedusing a code with a length of L_(C)=4, and it is determined based onequation (8) that the total transmission power is equal to 4, then noincrease in transmission power resulted from multiplexing the signallayers together.

At step S128, it is determined whether the current layer value is equalto the total number of M layers. If the current layer value is not equalto M, resulting in a “no” at step S128, then step S132 is performed. Atstep S132, the current layer value is incremented by one, and theprocess returns to step S124 to repeat steps S124, S126, S127, and S128for a subsequent layer. As shown in FIG. 1A, the process repeats until afourth layer including data12, data13, data14, and data15 have beenmultiplexed onto the previous three layers by adding each of the bits ofthe spread signal from the fourth layer to the bits from the previousthree layers. Otherwise, if the current layer value is equal to M,resulting in a “yes” at step S128, then step S130 is performed.

At step S130, the multi-layer multiplexed signal is allocated to one ormore subcarriers. For example, the four bits that include data from thefirst to the fourth layers are allocated to the 0^(th) to 3^(rd)subcarriers, which results in sixteen symbols being multiplexed ontofour subcarriers. The transmitter modulation process 120 is repeated for512 (=2048/4) groups of subcarriers, which according to equation (1)results in 8192 symbols (=2048/4×4×4) being multiplexed for one inversefast Fourier transform (IFFT) of the transmitter 100. In oneimplementation where quadrature phase-shift keying (QPSK) is performedon one symbol, the number of bits in one symbol, N_(b), is equal to two.As a result, eight bits are multiplexed for each subcarrier, which isequal to the number of transmitting bits for 256 quadrature amplitudemodulation-orthogonal frequency-division multiplexing (QAM-OFDM).

FIG. 2A is an exemplary block diagram of a receiver 200, according tocertain embodiments. The receiver 200 includes an antenna 202 thatreceives signals, RF front end 204 that converts the incoming RF signalto baseband, and a CP removal module 206 that removes the CP from theincoming signal. The received signal is then returned to the frequencydomain at fast Fourier transform (FFT) block 208. In one implementation,the resultant frequency domain signal is denoted by Rx M.

FIG. 2A also shows a diagram that illustrates how a layered, multiplexedsignal is received and recovered by the receiver 100. In someimplementations, the receiver 200 includes circuitry that is configuredto perform a demodulation process that includes reverse spreading thereceived signal to recover the transmitted symbols. The reversespreading is performed for each group of L_(C) subcarriers using theorthogonal codes cd0 to cd(L_(C)−1), which recovers L_(C) receivedsymbols from the M^(th) layer. The received symbols are then spreadagain using the orthogonal codes cd0 to cd(L_(C)−1), and the resultantspread signal is multiplied by coefficient cg M. After themultiplication, the resultant signal is subtracted from the originalsignal Rx M, and signal Rx (M−1) is obtained. Next, the reversespreading process with the orthogonal codes cd0 to cd(L_(C)−1) is againapplied to the signal Rx (M−1), and another set of L_(C) symbols areobtained for the (M−1)th layer. Subsequently, the demodulation processis repeated until the 1^(st) layer is reached, and all transmittedsymbols are demodulated. The receiver 200 then repeats the demodulationprocess to recover the transmitted symbols allocated to each subcarrier.

FIG. 2B is an exemplary flowchart of a receiver demodulation process220, according to certain embodiments. In one example, the number ofsubcarriers N_(sub) that can be handled by the FFT block 208 of thereceiver 200 is equal to 2048. In addition, a total number of layers Massociated with the symbols to be recovered is equal to 4.

At step S222 a current layer value is initialized to a value of M, whichis 4 in one example. At step S224, a received signal Rx M associatedwith the first L_(C) number of subcarriers SC0 to SC3 is reverse spreadvia the orthogonal codes cd0, cd1, cd2, and cd3 to recover the spreadsymbols associated with a highest layer of the transmit signal. As shownin FIG. 2A, data(n+12), data(n+13), data(n+14), and data(n+15) arerecovered by performing the reverse spreading on the received signal Rx4, which are the spread data signals that were allocated to the fourth,or highest, layer of the transmit signal.

At step S226, the recovered signals are re-spread using the orthogonalcodes cd0, cd1, cd2, and cd3 and are multiplied by the coefficient cg3.As discussed previously, the received signal Rx M includes signals thatare spread over the 1^(st) to the M^(th) layers by using the sameorthogonal codes to spread the signals, which means that the layers arenon-orthogonal with respect to one another. By modifying the amplitudes,each of the layers can be recovered at the receiver by applying thecorresponding coefficients that were used at the transmitter 100. Asdiscussed previously, when the M^(th) layer is reverse spread, to reduceinterference between the M^(th) layer and the 1^(st) to (M−1)^(th)layers, the layer coefficients are determined based on equation (4). Theresultant highest received signal layer that is multiplied by cg3 isthen subtracted from the Rx 4 signal to obtain the Rx 3 signal thatincludes the remaining lower signal layers. For example, the Rx 3 signalincludes the spread signals associated with the first, second, and thirdlayers.

At step S228, it is determined whether the current layer value is equalto one. If the current layer value is not equal to one, resulting in a“no” at step S228, then step S230 is performed. At step S230, thecurrent layer value is decremented by one, and the process returns tostep S224 to repeat steps S224, S226, and S228 in order to recover thereceived symbols associated with the next lowest layer. As shown in FIG.2A, the process repeats until the transmitted symbols for the third,second, and first layers have been recovered. Otherwise, if the currentlayer value is equal to 1, resulting in a “yes” at step S228, then theprocess is terminated. The receiver demodulation process 400 isperformed for all subcarriers to recover all of the transmitted data,which include the 512 groups of four subcarriers for the exampledescribed herein.

FIGS. 3A and 3B are exemplary diagrams multiplexed layers resulting fromthe transmitter modulation process 120, according to certainembodiments. FIG. 3A illustrates an implementation where a first layerand a second layer employing QPSK that are multiplexed with the samephase. In FIG. 3B, the second layer is added to the first layer at anoffset of 45 degrees. In some embodiments, the offset is added to everyother layer of the multiplexed signal. For example, the fourth and sixthlayers are also offset at 45 degrees. For the layers that have theoffset applied, the layer coefficients cg are complex numbers, resultingin an overall amplitude reduction for the offset layers and reducedtransmit power when compared to multiplexed signals that do not have theoffset applied.

FIG. 4A is an exemplary graph of bit error rate BER of a physical layer(PHY BER), according to certain embodiments. The graph shows exemplaryBER values for the transmitter 100 and receiver 200 described hereinwith respect to energy per bit to noise power spectral density(E_(b)/N₀) and includes theoretical values for QPSK and 256QAM systems.In addition, for BER curves shown in FIG. 4A, a Walsh code of lengthL_(C)=4 is used, and a total number of multiplexed layers is equal tofour. In addition, OFDM with 2048 subcarriers is assumed, and allsubcarriers are QPSK modulated, according to one implementation. BERcurves are illustrated for cases where dlt is equal to 0.2, 0.3, 0.4,and 0.5, which show that the BER improves as the value of dlt increases.When dlt is equal to 0.4, the resulting BER is approximately equal tothe BER for QPSK. The graph also includes a BER curve for a dlt of 0.5,which shows that the BER improvement for dlt values of greater than 0.4is reduced due to saturation. Because the subcarriers areQPSK-modulated, the physical layer BER may not decrease to be less thanthe BER for QPSK.

FIG. 4B is another exemplary graph of BER of a physical layer, accordingto certain embodiments. FIG. 4B also includes the theoretical values forQPSK and 256QAM systems as well as BER curves for the transmitter 100and receiver 200 with a Walsh code of length L_(C)=4, four multiplexedlayers, and dlt values of 0.2, 0.3, and 0.4. In addition, OFDM with 2048subcarriers is assumed, and all subcarriers are QPSK modulated. FIG. 4Balso includes an offset BER curve for an implementation where dlt isequal to 0.3, and an offset of 45 degrees is added to alternatinglayers, such as a second layer and a fourth layer, and the four layersare multiplexed together according to the processes describedpreviously. The offset BER curve is approximately equal to thetheoretical QPSK BER curve, but the amplitude of the offset multiplexedsignal is a factor of 0.2 less than the amplitude of a multiplexedsignal without an offset.

FIGS. 4A and 4B both illustrate that a communication capacitycorresponding to the capacity of 256QAM can be fulfilled at E_(b)/N₀values corresponding to E_(b)/N₀ of QPSK. For example, with 256QM-OFDM,in order to achieve a PHY BER of 10⁻³ an environment E_(b)/N₀ isapproximately equal to 18 dB. However, according to the embodimentsdescribed herein, a 10⁻³ BER can be achieved at an environment E_(b)/N₀of approximately 7 dB. According to some implementations, urbanenvironments have E_(b)/N₀ values of 10 to 15 dB, which means that256QAM may not be able to be used. However, since the embodimentsdescribed herein ensure that transmission rates corresponding to 256QAMcan be achieved while maintaining an E_(b)/N₀ of approximately 7 dB,frequency utilization efficiency may be quadrupled, and signals in theurban areas with E_(b)/N₀ values of 10 to 15 dB can be successfullytransmitted.

In addition, the receiver 200 performs reverse spreading and subtractionof the multiplexed layers of the received signal, and interferencebetween the layers is reduced based on the layered coefficient cgdeterminations described previously. Also, PSK modulation may be usedfor each of the layers higher than or equal to the second layer becausethe signal information may only be included in the phase. For example,QPSK corresponds to 4 PSK. By using phase-shift keying (PSK) for thesecond and higher layers, the multi-level modulation does not interferewith the first layer.

Employing PSK for one or more layers of the multiplexed signal allows agreater number of total symbols to be communication by one IFFT of thetransmitter 100 and one FFT of the receiver 200. For example, in thecase where M is equal to four layers, QPSK is applied to each of thesecond to fourth layers, and 16QAM is applied to the first level,resulting in 13 bits being transmitted per subcarrier, which correspondsto 8192QAM. The PHY BER associated with the multiplexed signal with 13bits per subcarrier is greater than the PHY BER for QPSK, but is alsoless than the BER for QAM signals.

According to certain embodiments, multiplexing is performedsimultaneously with increasing the amplitude of each of the signallayers, resulting in an increase of peak-to-average power ratio (PAPR).The increased PAPR of the multiplexed signal may make linearity of atransmission power amplifier (PA) in the transmitter 100 moresignificant. For example, when there is no offset for a singlemultiplexed signal with OFDM, the PAPR is 8.8 dB. For a case where fourlayers are multiplexed together according to the processes describedherein, the PAPR is approximately 9.8 dB, resulting in a PAPR increaseof 1 dB. The PAPR increase resulting from the four multiplexed layersmay not cause a maximum transmission power to be exceeded for a basestation transmitting a downlink (DL) signal, but terminal devices, suchas cell phones or other mobile devices, may not be able to accommodatethe increased PAPR. In some implementations, the issues caused by thePAPR increase at the terminal can be reduced by increasing a maximumtransmit power at the terminal device, applying SC-OFDM, furtherapplying distortion compensation, and the like.

According to certain embodiments where an uplink (UL) signal istransmitted from a terminal device to a base station, a plurality ofterminal devices use the same subcarrier, which causes the transmitterson the terminal devices to control the transmit power so that thesignals received at the base station maintain the relationshipsaccording to equation (8). By executing the processes described herein,the transmitter 100 on the terminal devices can decrease the totalnumber of subcarriers when transmitting a multiplexed signal so that theterminal device may not need to perform power control operations. Forexample, in LTE, a minimum transmission size includes a group of 12subcarriers per resource block (RB). When subcarrier modulation isperformed by QPSK, 24 bits can be transmitted, and when subcarriermodulation is performed by 16QAM, 48 bits can be transmitted.

By contrast, according to the embodiments described herein, when foursubcarriers are allocated to each terminal device and four iterations ofthe transmitter modulation process 120 are performed to multiplex fourlayers together using QPSK and 8 bits per subcarrier, 32 bits can betransmitted by the transmitter 100. Also, where the modulation schemeincludes 16QAM for the first layer and 8 PSK for the second throughfourth layers with 13 bits per subcarrier, 52 bits can be transmitted.In this example, three terminal devices can be allocated to one resourceblock, which triples the total capacity of the resource block becauseeach terminal device is using just four subcarriers of the 12-subcarrierresource block. Therefore, reducing the subcarrier allocation for eachterminal device by performing the layered multiplexing processesdescribed herein, greater numbers of signals can be multiplexed andtransmitted by the terminal devices without having to restricttransmission power.

According to the embodiments described herein, frequency utilizationefficiency can be increased by sequentially multiplexing signalsresulting from orthogonal multiplexing using an orthogonal code whilesimultaneously modifying the amplitudes of the signals. By performingthe processes described herein, transmission rates corresponding to256QAM can be achieved while maintaining PHY BER values corresponding tothose of QPSK. Quadrupling the frequency utilization efficiency allowswireless communication systems to accommodate future growth in wirelesscommunication traffic.

A hardware description of an exemplary device 500 for performing one ormore of the embodiments described herein is described with reference toFIG. 5. For example, the hardware described by FIG. 5 can apply to acellular base station and/or a terminal device, which can include anytype of mobile device that communicates via at least one wirelessnetwork. When the device 500 is programmed to perform the processesrelated signal modulation and demodulation described herein, the device500 becomes a special purpose device.

The device 500 includes a RF transceiver 526 that includes thecomponents and circuitry of the transmitter 100 and receiver 200described previously. The transceiver 526 can include a transmit antennaand a receive antenna, or the transmitter 100 and receiver 200 can sharea common antenna with associated isolation components, such as a fullduplexer. In other implementations, the device 500 can include just thetransmitter 100 or just the receiver 200.

The device 500 includes a CPU 500 that perform the processes describedherein. The process data and instructions may be stored in memory 502.These processes and instructions may also be stored on a storage mediumdisk 504 such as a hard drive (HDD) or portable storage medium or may bestored remotely. Further, the claimed advancements are not limited bythe form of the computer-readable media on which the instructions of theinventive process are stored. For example, the instructions may bestored on CDs, DVDs, in FLASH memory, RAM, ROM, PROM, EPROM, EEPROM,hard disk or any other information processing device with which thedevice 500 communicates, such as a terminal device and/or base station.

Further, the claimed advancements may be provided as a utilityapplication, background daemon, or component of an operating system, orcombination thereof, executing in conjunction with CPU 500 and anoperating system such as Microsoft Windows, UNIX, Solaris, LINUX, AppleMAC-OS and other systems known to those skilled in the art.

CPU 500 may be a Xenon or Core processor from Intel of America or anOpteron processor from AMD of America, or may be other processor typesthat would be recognized by one of ordinary skill in the art.Alternatively, the CPU 500 may be implemented on an FPGA, ASIC, PLD orusing discrete logic circuits, as one of ordinary skill in the art wouldrecognize. Further, CPU 500 may be implemented as multiple processorscooperatively working in parallel to perform the instructions of theinventive processes described above.

The device 500 in FIG. 5 also includes a network controller 506, such asan Intel Ethernet PRO network interface card from Intel Corporation ofAmerica, for interfacing with network 528. As can be appreciated, thenetwork 528 can be a public network, such as the Internet, or a privatenetwork such as an LAN or WAN network, or any combination thereof andcan also include PSTN or ISDN sub-networks. The network 528 can also bewired, such as an Ethernet network, or can be wireless such as acellular network including EDGE, 3G and 4G wireless cellular systems.The wireless network can also be Wi-Fi, Bluetooth, or any other wirelessform of communication that is known.

The device 500 further includes a display controller 508 for interfacingwith display 510 of the device 500, such as an LCD monitor. A generalpurpose I/O interface 512 at the device 500 interfaces with a keyboardand/or mouse 514 as well as a touch screen panel 516 on or separate fromdisplay 510. General purpose I/O interface 512 also connects to avariety of peripherals 518 including printers and scanners.

The general purpose storage controller 524 connects the storage mediumdisk 504 with communication bus 526, which may be an ISA, EISA, VESA,PCI, or similar, for interconnecting all of the components of the device500. A description of the general features and functionality of thedisplay 510, keyboard and/or mouse 514, as well as the displaycontroller 508, storage controller 524, network controller 506, soundcontroller 520, and general purpose I/O interface 512 is omitted hereinfor brevity as these features are known.

The exemplary circuit elements described in the context of the presentdisclosure may be replaced with other elements and structureddifferently than the examples provided herein. Moreover, circuitryconfigured to perform features described herein may be implemented inmultiple circuit units (e.g., chips), or the features may be combined incircuitry on a single chipset, as shown on FIG. 6.

FIG. 6 shows a schematic diagram of a data processing system, accordingto certain embodiments, for performing the transmitter modulationprocess 120 and/or the receiver demodulation process 220. The dataprocessing system is an example of a computer in which code orinstructions implementing the processes of the illustrative embodimentsmay be located.

In FIG. 6, data processing system 600 employs a hub architectureincluding a north bridge and memory controller hub (NB/MCH) 625 and asouth bridge and input/output (I/O) controller hub (SB/ICH) 620. Thecentral processing unit (CPU) 630 is connected to NB/MCH 625. The NB/MCH625 also connects to the memory 645 via a memory bus, and connects tothe graphics processor 650 via an accelerated graphics port (AGP). TheNB/MCH 625 also connects to the SB/ICH 620 via an internal bus (e.g., aunified media interface or a direct media interface). The CPU Processingunit 630 may contain one or more processors and even may be implementedusing one or more heterogeneous processor systems.

For example, FIG. 7 shows one implementation of CPU 630. In oneimplementation, the instruction register 738 retrieves instructions fromthe fast memory 740. At least part of these instructions are fetchedfrom the instruction register 738 by the control logic 736 andinterpreted according to the instruction set architecture of the CPU630. Part of the instructions can also be directed to the register 732.In one implementation the instructions are decoded according to ahardwired method, and in another implementation the instructions aredecoded according a microprogram that translates instructions into setsof CPU configuration signals that are applied sequentially over multipleclock pulses. After fetching and decoding the instructions, theinstructions are executed using the arithmetic logic unit (ALU) 734 thatloads values from the register 732 and performs logical and mathematicaloperations on the loaded values according to the instructions. Theresults from these operations can be feedback into the register and/orstored in the fast memory 740. According to certain implementations, theinstruction set architecture of the CPU 630 can use a reducedinstruction set architecture, a complex instruction set architecture, avector processor architecture, a very large instruction wordarchitecture. Furthermore, the CPU 630 can be based on the Von Neumanmodel or the Harvard model. The CPU 630 can be a digital signalprocessor, an FPGA, an ASIC, a PLA, a PLD, or a CPLD. Further, the CPU630 can be an x86 processor by Intel or by AMD; an ARM processor, aPower architecture processor by, e.g., IBM; a SPARC architectureprocessor by Sun Microsystems or by Oracle; or other known CPUarchitecture.

Referring again to FIG. 6, the data processing system 600 can includethat the SB/ICH 620 is coupled through a system bus to an I/O Bus, aread only memory (ROM) 656, universal serial bus (USB) port 664, a flashbinary input/output system (BIOS) 668, and a graphics controller 658.PCI/PCIe devices can also be coupled to SB/ICH YYY through a PCI bus662.

The PCI devices may include, for example, Ethernet adapters, add-incards, and PC cards for notebook computers. The Hard disk drive 660 andCD-ROM 666 can use, for example, an integrated drive electronics (IDE)or serial advanced technology attachment (SATA) interface. In oneimplementation the I/O bus can include a super I/O (SIO) device.

Further, the hard disk drive (HDD) 660 and optical drive 666 can also becoupled to the SB/ICH 620 through a system bus. In one implementation, akeyboard 670, a mouse 672, a parallel port 678, and a serial port 676can be connected to the system bust through the I/O bus. Otherperipherals and devices that can be connected to the SB/ICH 620 using amass storage controller such as SATA or PATA, an Ethernet port, an ISAbus, a LPC bridge, SMBus, a DMA controller, and an Audio Codec.

Moreover, the present disclosure is not limited to the specific circuitelements described herein, nor is the present disclosure limited to thespecific sizing and classification of these elements. For example, theskilled artisan will appreciate that the circuitry described herein maybe adapted based on changes on battery sizing and chemistry, or based onthe requirements of the intended back-up load to be powered.

The functions and features described herein may also be executed byvarious distributed components of a system. For example, one or moreprocessors may execute these system functions, wherein the processorsare distributed across multiple components communicating in a network.The distributed components may include one or more client and servermachines, which may share processing in addition to various humaninterface and communication devices (e.g., display monitors, smartphones, tablets, personal digital assistants (PDAs)). The network may bea private network, such as a LAN or WAN, or may be a public network,such as the Internet. Input to the system may be received via directuser input and received remotely either in real-time or as a batchprocess. Additionally, some implementations may be performed on modulesor hardware not identical to those described. Accordingly, otherimplementations are within the scope that may be claimed.

The above-described hardware description is a non-limiting example ofcorresponding structure for performing the functionality describedherein. In other alternate embodiments, processing features according tothe present disclosure may be implemented and commercialized ashardware, a software solution, or a combination thereof. Moreover,instructions corresponding to the transmitter modulation process 120and/or receiver demodulation process 220 in accordance with the presentdisclosure could be stored in a thumb drive that hosts a secure process.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of this disclosure. For example, preferableresults may be achieved if the steps of the disclosed techniques wereperformed in a different sequence, if components in the disclosedsystems were combined in a different manner, or if the components werereplaced or supplemented by other components. The functions, processesand algorithms described herein may be performed in hardware or softwareexecuted by hardware, including computer processors and/or programmablecircuits configured to execute program code and/or computer instructionsto execute the functions, processes and algorithms described herein.Additionally, an implementation may be performed on modules or hardwarenot identical to those described. Accordingly, other implementations arewithin the scope that may be claimed.

The above disclosure also encompasses the embodiments listed below.

(1) A device includes circuitry configured to spread one or more symbolswith one or more orthogonal codes into spread signals having apredetermined number of bits, modify an amplitude of the spread signalsvia one or more layer coefficients, and multiplex the spread signalsinto a layered transmit signal.

(2) The device of (1), wherein the circuitry is further configured toallocate the layered transmit signal to a predetermined number ofsubcarriers.

(3) The device of (1) or (2), wherein the predetermined number ofsubcarriers corresponds to the predetermined number of bits of thespread signal.

(4) The device of any one of (1) to (3), wherein the one or moreorthogonal codes are Walsh codes.

(5) The device of any one of (1) to (4), wherein the circuitry isfurther configured to determine the layer coefficients based on acoefficient difference factor that is less than one.

(6) The device of any one of (1) to (5), wherein the circuitry isfurther configured determine a highest layer coefficient to be greaterthan a sum of one or more remaining lower layer coefficients.

(7) The device of any one of (1) to (6), wherein the circuitry isfurther configured to reduce a physical layer bit error rate byincreasing the coefficient difference factor.

(8) The device of any one of (1) to (7), wherein the circuitry isfurther configured to modify a total transmit power by modifying atleast one of a sum of the layer coefficients or the predetermined numberof bits of the spread signal.

(9) The device of any one of (1) to (8), wherein the circuitry isfurther configured to reduce a total transmit power for the layeredtransmit signal by adding an offset to at least one of the one or morelayer coefficients.

(10) The device of any one of (1) to (9), wherein the circuitry isfurther configured to add the offset to alternating layers of thelayered transmit signal.

(11) The device of any one of (1) to (10), wherein the offset is equalto 45 degrees.

(12) The device of any one of (1) to (11), wherein the layered transmitsignal includes one or more non-orthogonal signal layers.

(13) The device of any one of (1) to (12), wherein the circuitry isfurther configured to reduce interference between the one or morenon-orthogonal signal layers by modifying the amplitude of the spreadsignals with the one or more layer coefficients.

(14) The device of any one of (1) to (13), wherein the circuitry isfurther configured to implement quadrature amplitude modulation for afirst layer and phase-shift keying modulation for second and higherlayers of the layered transmit signal.

(15) The device of any one of (1) to (14), wherein the circuitry isfurther configured to allocate signals from one terminal device to foursubcarriers of a twelve-subcarrier resource block.

(16) The device of any one of (1) to (15), wherein the circuitry isfurther configured to recover a highest received signal layers byreverse spreading a received signal with the one or more orthogonalcodes.

(17) The device of any one of (1) to (16), wherein the circuitry isfurther configured to re-spread the highest received signal layer withthe one or more orthogonal codes and multiply a corresponding spreadsignal by an associated layer coefficient.

(18) The device of any one of (1) to (17), wherein the circuitry isfurther configured to subtract a re-spread signal from the receivedsignal to recover one or more lower received signal layers.

(19) A method including: spreading one or more symbols with one or moreorthogonal codes into spread signals having a predetermined number ofbits; modifying an amplitude of the spread signals via one or more layercoefficients; and multiplexing the spread signals into a layeredtransmit signal.

(20) A device including: circuitry configured to recover a highestreceived signal layer by reverse spreading a received signal with theone or more orthogonal codes, re-spread the highest received signallayer with one or more orthogonal codes and multiply a correspondingspread signal by an associated layer coefficient, and subtract are-spread signal from the received signal to recover one or more lowerreceived signal layers.

The invention claimed is:
 1. A device comprising: circuitry configuredto spread symbols with orthogonal codes into spread signals having apredetermined number of bits, modify an amplitude of the spread signalsvia layer coefficients, and multiplex the amplitude modified spreadsignals into a layered transmit signal; and a communication interfaceconfigured to transmit the layered transmit signal, wherein thecircuitry is configured to determine the layer coefficients based on acoefficient difference factor that is less than one, and determine ahighest layer coefficient to be greater than a sum of a plurality ofremaining lower layer coefficients.
 2. The device of claim 1, whereinthe circuitry is further configured to allocate the layered transmitsignal to a predetermined number of subcarriers.
 3. The device of claim2, wherein the predetermined number of subcarriers corresponds to thepredetermined number of bits of the spread signal.
 4. The device ofclaim 1, wherein the orthogonal codes are Walsh codes.
 5. The device ofclaim 1, wherein the circuitry is further configured to reduce aphysical layer bit error rate by increasing the coefficient differencefactor.
 6. The device of claim 1, wherein the circuitry is furtherconfigured to modify a total transmit power by modifying at least one ofa sum of the layer coefficients or the predetermined number of bits ofthe spread signal.
 7. The device of claim 1, wherein the circuitry isfurther configured to reduce a total transmit power for the layeredtransmit signal by adding an offset to at least one of the layercoefficients.
 8. The device of claim 7, wherein the circuitry is furtherconfigured to add the offset to alternating layers of the layeredtransmit signal.
 9. The device of claim 8, wherein the offset is equalto 45 degrees.
 10. The device of claim 1, wherein the layered transmitsignal includes non-orthogonal signal layers.
 11. The device of claim10, wherein the circuitry is further configured to reduce interferencebetween the non-orthogonal signal layers by modifying the amplitude ofthe spread signals with the layer coefficients.
 12. The device of claim1, wherein the circuitry is further configured to implement quadratureamplitude modulation for a first layer and phase-shift keying modulationfor second and higher layers of the layered transmit signal.
 13. Thedevice of claim 1, wherein the circuitry is further configured toallocate signals from one terminal device to four subcarriers of atwelve-subcarrier resource block.
 14. The device of claim 1, wherein thecircuitry is further configured to recover a highest received signallayers by reverse spreading a received signal with the orthogonal codes.15. A device comprising: circuitry configured to spread symbols withorthogonal codes into spread signals having a predetermined number ofbits, modify an amplitude of the spread signals via layer coefficients,and multiplex the amplitude modified spread signals into a layeredtransmit signal; and a communication interface configured to transmitthe layered transmit signal, wherein the circuitry is configured torecover a highest received signal layer by reverse spreading a receivedsignal with the orthogonal codes, and re-spread the highest receivedsignal layer with the orthogonal codes and multiply a correspondingspread signal by an associated layer coefficient.
 16. The device ofclaim 15, wherein the circuitry is further configured to subtract are-spread signal from the received signal to recover one or more lowerreceived signal layers.
 17. A method comprising: spreading symbols withorthogonal codes into spread signals having a predetermined number ofbits; modifying an amplitude of the spread signals via layercoefficients; and multiplexing the amplitude modified spread signalsinto a layered transmit signal; transmitting the layered transmitsignal, wherein the layer coefficients are determined based on acoefficient difference factor that is less than one, and a highest layercoefficient to be greater than a sum of a plurality of remaining lowerlayer coefficients.